The miracle of Ascension: watching tearful turtles as they nest on a remote volcanic island
Turtles swim thousands of miles to Ascension Island where they shed tears as they lay eggs during a nesting ritual. In a new book, Stewart McPherson describes watching the intimate spectacle
Islands are not merely lumps of rock surrounded by water, but crucibles of evolution; powerful engines that drive the evolutionary development of the few plants and animals that reach their shores and survive. Sometimes, however, it’s the creatures that shape the land. Whilst exploring the cinder cones of Ascension Island in the southern Atlantic, 1,000 miles from the coast of Africa, I noticed that the few sandy beaches were strangely pitted with thousands of small craters. These are made by female green sea turtles which come to Ascension each year from January to June to clamber on to the beaches and lay their eggs. The island is one of the world’s most important breeding grounds for this endangered species. Around 5,000 turtles visit each year and each turtle nests on average six times per season. They quickly came to the attention of the first colonial travellers. Over the 18th and 19th centuries, the abundant turtles were increasingly hunted. Some were kept in manmade “turtle ponds” for months, providing a steady supply of meat.
By the 1860s, the population had shrunk dramatically; only a few hundred turtles could be found each season. The rapid population decline stemmed from the extreme fragility of the turtles’ breeding habits. It is estimated that just one in 1,000 turtle hatchlings survive to maturity. Female green turtles do not start reproducing until they are approximately 20 years old, and then only once every three or four years. The removal of the breeding individuals caused a swift population collapse, especially since the females were usually killed before they had even completed laying their first clutch of eggs. From 1901, the harvesting of turtles was restricted, and by the 1920s the trade had virtually stopped. The ponds fell out of use. The turtles of Ascension Island are now strictly protected. Over the past 60 years, the population of green turtles of Ascension Island has rebounded spectacularly.
The nesting spot
One evening, an hour or so after sunset, I joined the Ascension Island Government Conservation Department’s turtle team to observe dozens of females nesting. I could see each animal clambering onto the beach and slowly moving about 20 to 50m above the high-tide mark. Each turtle moved awkwardly on land, lurching forward as she pulled with her flippers, then stopped to rest for a few seconds under the strain of her own, tremendous body weight. The turtles usually lumbered up the beach in a straight line, but sometimes they zig-zagged erratically. Some would fail to find a suitable place to nest and then return to the water without laying. Most found what they were looking for and began flicking sand backwards with their flippers. I was instructed to approach the turtles carefully from behind, to sit still and remain out of the turtles’ field of vision. Several times, I underestimated how powerful the turtles’ flippers were; sitting behind a great turtle, several kilograms of sand were thrown into the air to land on top of me. The turtles would dig for up to an hour, making several flipper strokes at a time before resting, then dig for another round between deep, hissing breaths.
As the hours passed by, I counted over a dozen turtles within my field of vision, each discernible in tones of red in the dim light that melted away into the inky shadows of the pitted beach. When each nest chamber had been excavated to a depth of 50 to 70 cm, each turtle would use her sensitive rear flippers to test the sand by shuffling it backwards and forwards, ensuring the correct consistency and depth. Despite all of their efforts, some would decide their site was not suitable after all and abandoned it in favour of returning another night. The majority seemed satisfied and began laying.
Tears of a turtle
Each animal would enter a trance-like state and become oblivious to bystanders. From the cloaca under her tail, up to 150 ping pong ball-sized white eggs would gently drop into the nest hole. It was easy to see how vulnerable the nesting females were to the hungry sailors during this stage of nesting. As the eggs are laid, streams of tears flow from the turtle’s eyes. Early observers romantically suggested that each turtle cries over abandoning her eggs and never knowing her offspring, but the scientific explanation is more utilitarian; the tears emanate from a gland that removes salt from sea water, enabling turtles to drink. Eventually, after all of the eggs are released, the turtle uses her back flippers to cover the eggs gently with sand. She then flicks sand from the side of the crater to hide the exact spot where she has laid her clutch of eggs. The crater may be moved forward by a couple of metres to disguise the location of the nest itself, and in doing so, prevents other turtles from dropping into the original crater and digging up the nests of previous visitors.
With the job finally done, the exhausted turtle slowly returns to the sea. An hour before dawn, I could see dozens of turtles lumbering back down the beach. Each one left behind a distinctive trail with regular imprints from their flippers. The trails resemble those of giant tractor tyres or military tanks. On reaching the water, the turtles transform in an instant. Invigorated by the waves rushing over their bodies, the turtles push forward energetically. As soon as their bodies are buoyed by the water, the turtles glide forward effortlessly through the waves and surf. The contrast between their awkwardness on land and their agility in the water is marked.
No food ’til Brazil
As dawn broke, I was astounded to see that hundreds of turtle tracks were visible. Each morning, the conservationists rake the beaches to monitor the population recovery, and count the visits. During the height of the season, up to 400 turtles may clamber onto Long Beach each night, depositing several million eggs in Ascension’s sands each season. Once back in the water, the turtles rest before laying further clutches. Each lays between four to eight clutches each season, with an average of six clutches per animal and two weeks between each clutch. When all of the eggs have been laid, the turtles migrate back to Brazil. Amazingly, the turtles do not eat while they are on Ascension as their regular food sources, seaweeds and sea grasses, are not found in the island’s waters. It is thought that by resting close to shore in between their nesting events, the turtles conserve energy for laying and then migrating at the end of their nesting season. The female turtles repeat their journey to Ascension Island every three to four years, making as many as 10 journeys back to the island during their lifetime, though it is thought male turtles visit the island more frequently.
Eruption of life
On average, each clutch of eggs hatches six to eight weeks after being laid. When ready to hatch, the buried eggs rupture almost simultaneously. It is still not understood how hatching takes place in almost perfect unison. The hatchlings dig through the layer of compacted sand above them, a task that can take a number of days and then they stop close to the surface, possibly waiting for the sand to cool, indicating the arrival of night. They then poke their heads through the surface of the sand and, all of a sudden, the nest erupts and a torrent of hatchlings cascades forth. Despite arriving just before morning, I had the good fortune to stumble upon a nest just as the process was beginning.
The word “eruption” perfectly captures the frenzy of activity. Up to 150 baby turtles frenetically scramble across the sand, scurrying over and past each other. Their flailing flippers propel them forwards, up over the rim of the nest and directly towards the sea. They are perfect miniatures of adult turtles, although their shells are not yet hard. Their movements are frantic, furious and unrelenting, reminding me of a child’s clockwork mechanical toy. They desperately race to reach the water, their urgency being to escape land-based predators. How they naturally detect the location of the water is hard to imagine. It has been suggested that they instinctively respond to light sparkling on the waves, the sound of the water, the scent of the ocean, or they naturally orient themselves to clamber downhill. For a few minutes, a stream of turtle hatchlings rushes forth from each nest, ending with a few last stragglers before stillness returns.
Death on wings
Young turtles are extremely vulnerable. I observed a few stragglers still scampering down the beach an hour after sunrise. These latecomers face real danger. Their dark shells are conspicuous against the bright sand and the commotion of the earlier wave of hatchlings has usually attracted the attention of predators. Ascension frigatebirds patrolled the skies, swooping down to snatch the stragglers. The frigates’ black, W-shaped wings, forked V-shaped tails, great size, glaring black eyes and long, hooked, razor-sharp beaks formed a picture of pure terror in the skies above. I will not forget the image of a baby turtle being carried through the air by its flipper by one of the birds, frantically struggling in vain. The hatchlings were being carried off to be torn apart just minutes after emerging into the world.
As a naturalist, one should not sentimentalise events like this, yet I could not help but feel sorry for the young turtles, snatched away by winged death at the start of their journey. It is the circle of life, however, and the frigatebirds – along with crabs, black triggerfish, sharks, rays and larger predatory fish – gain a much needed meal. Within the first few hours, a large proportion may be eaten. Despite the losses, that sea turtles choose distant islands to nest is not surprising. Remote oceanic islands such as Ascension generally lack large terrestrial predators, particularly large mammals, and offer beaches that are safe for mothers and hatchlings alike. A few nests may be flooded by the sea, eroded by wave action or accidentally excavated by other nesting turtles, but the overwhelming majority of egg clutches laid on Ascension hatch successfully.
This is an edited extract from Britain’s Treasure Islands: A Journey to the UK Overseas Territories by Stewart McPherson, published by Redfern Natural History Productions (£29.99), on sale now. McPherson thanks Lord Ashcroft for donating a copy of the book to every UK secondary school